a report from our chief science correspondent, robert bazell. >> reporter: jenna, like many moms, worries about producting her young kids from chemical contamination. especially the effects of the the chemical, bpa, found in plastics. >> i'm avoiding plastic in general. we try to drink out of glass. all of our water bottles, we take away with us, are reuseable. they're glass or metal. >> reporter: a new study suggests that moms may be passing along effects of bpa to their kids. in a study of 500 pregnant women, those with the highest levels of bpa have lower thyroid levels. and so did their infant sons. why only boys? scientists aren't sure. but they see the same thing in animal studies. thyroid hormones help control many systems in the body and can affect childhood development. >> if bpa is affecting the levels during pregnancy, this could be affecting the learning, memory and behavior of children later in life. >> reporter: bpa is part of many widely used plastic products. including can liners in certain bottles. most americans have trace amounts in their body. while there have been man